The present invention relates to a method of operating a communications network and in particular to method of determining the performance of a wireless communications network
There is a developing trend for voice and data communications to be more available and to be made using a wider range of devices. An example of this is the ability to make voice over IP (VoIP) calls using a range of devices, such as mobile phones, PDAs, laptop computers, etc. Such calls may be routed via domestic wireless access points (WAPs) or via a publicly accessible WAP, such as those provided as a part of the applicant's BT Openzone™ service, for example using WiFi technology (standardised in the IEEE 802.11 family of standards).
For any wireless communication system the available capacity must be shared between all those who wish to use it and an excessive number of users, amount of traffic or type of traffic may lead to poor quality of service. For example, WiFi uses a Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol: a mobile terminal that wishes to send a packet will monitor the wireless channel for a predetermined period of time and if the channel is not in use by another terminal or the WAP then the terminal will send the packet. The terminal will then wait to received an acknowledgement signal from the WAP to indicate that the packet was received. If the acknowledgment signal is not received then the terminal will wait a longer period of time before sending any subsequent packets. It can be seen that if a number of terminals are sending a steady stream of packets, as would be the case when using VoIP over WiFi, then there may be a significant number of collisions between packets. This may then lead to all terminals to ‘back-of’ for an increasing period of time, which will lead to a further decrease in network efficiency and a decrease in voice quality for VoIP sessions.
A proposal to address this problem is disclosed by “An Adaptive IEEE 802.11 Scheme for Voice and Data Services in Wireless LANs”, C Li et al, IEEE Fifth Annual Conference on Communication Networks and Services Research (CNSR'07) in which the 802.11 standard is modified to include an adaptive algorithm such that real time traffic (such as VoIP) is handled differently from non-real time browsing (e.g. web surfing, downloads, etc.) such that the overall network performance is improved.
EP-A-1 836 066 discloses a jitter buffer controller which measures the jitter of received voice packets, compares the jitter values against a statistical distribution of jitter values and determines whether or not the jitter buffer is capable of absorbing the measured jitter of the received voice packet.
US2004/0073690 discloses a communications device which is able to collect one or more bandwidth-related metrics or parameters which can be associated with the audio quality of a voice communication session. If the metrics or parameters do not exceed a predetermined threshold then a voice communication session is not established.
According to a first aspect of the present invention there is provided a method of operating a wireless communications network, the method comprising the steps of: a) receiving a plurality of packets from a network node connected to the wireless communications network; b) determining a plurality of packet period parameter values, the packet period parameter being based on the time period between the reception of a packet and the reception of the subsequent packet; c) determining a plurality of jitter parameter values based on the variation of more than one packet period parameter values; and d) determining the performance of the wireless communications network in accordance with the ratio of the jitter parameter to the packet period parameter. Preferably, the method comprises the further step of e) taking corrective action if the ratio of the jitter parameter to the packet period parameter determined in step d) exceeds a predetermined ratio.
In one embodiment of the present invention a plurality of packets are received from a plurality of network nodes connected to the wireless communications network and the ratio of the jitter parameter to the packet period parameter is determined for the communication sessions associated with each of the plurality of network nodes. In such a case, step e) may comprises the step of not accepting any further communications sessions until ratio of the jitter parameter to the packet period parameter determined in step d) is less than an acceptable ratio and/or step e) may comprise terminating the communication sessions associated with one or more of the plurality of network nodes.
According to a second aspect of the present invention there is provided apparatus for use in a wireless communications network configured to, in use, receive a plurality of packets the wireless communications network; determine a plurality of packet period parameter values, the packet period parameter being based on the time period between the reception of a packet and the reception of the subsequent packet; determine a plurality of jitter parameter values based on the variation of more than one packet period parameter values; and determine the performance of the wireless communications network in accordance with the ratio of the jitter parameter to the packet period parameter. The may be further configured to, in use, take corrective action if the ratio of the jitter parameter to the packet period parameter exceeds a predetermined ratio.
According to a third aspect of the present invention there is provided a wireless access point comprising a wireless interface and an interface to a further network, the access point being configured in use to: i) receive one or more sessions from a wireless communication network, each session comprising a plurality of packets; and for each of the sessions: ii) determine a plurality of packet period parameter values, the packet period parameter being based on the time period between the reception of a packet and the reception of the subsequent packet; iii) determine a plurality of jitter parameter values based on the variation of more than one packet period parameter values; and iv) determine the performance of the wireless communications network in accordance with the ratio of the jitter parameter to the packet period parameter.
According to a fourth aspect of the present invention there is provided a computer product comprising computer executable code for the performance of a method as described above.